This invention relates to homopolymerization of mono-1-olefin monomers, such as ethylene and propylene, and copolymerization of a mono-1-olefin monomers, such as ethylene and propylene, with at least one higher alpha-olefin comonomer.
It is well known that mono-1-olefins, such as ethylene and propylene, can be polymerized with catalyst systems employing transition metals such as titanium, vanadium, chromium, nickel and/or other metals, either unsupported or on a support such as alumina, silica, titania, and other refractory metals. Supported polymerization catalyst systems frequently are used with a cocatalyst, such as alkyl boron and/or alkyl aluminum compounds. Organometallic catalyst systems, i.e., Ziegler-Natta-type catalyst systems usually are unsupported and frequently are used with a cocatalyst, such as methylaluminoxane.
It is also well-known that, while no polymer production process is easy, slurry, or loop, polymerization processes are relatively much more commercially desirable than other polymerization processes. Furthermore, the type of polymerization process used can have an effect on the resultant polymer. For example, higher reactor temperatures can result in low catalyst activity and productivity, as well as a lower molecular weight polymer product. Higher reactor pressures also can decrease the amount of desirable branching in the resultant polymer.
Most polymer products made in slurry processes, especially those polymer products made using supported chromium catalyst systems, have a broader molecular weight distribution and, therefore, the polymer product is much easier to process into a final product. Polymers made by other processes, such as, for example, higher temperature and/or higher pressure solution processes, can produce polymers having a narrow molecular weight distribution; these polymers can be much more difficult to process into an article of manufacture.
Unfortunately, many homogeneous organometallic catalyst systems have low activity, high consumption of very costly cocatalysts, like methylaluminoxane (MAO), and can produce low molecular weight polymers with a narrow molecular weight distribution. Furthermore, even though MAO can be necessary to produce a polymer with desired characteristics, an excess of MAO can result in decreased catalyst system activity. Additionally, these types of homogeneous catalyst systems preferably are used only in solution or gas phase polymerization processes.
It is an object of this invention to provide novel catalyst systems useful for polymerization.
It is another object of this invention to provide catalyst systems which are relatively simple to make, have increased activity and increased productivity.
It is a further object of this invention to provide catalyst systems which have reduced cocatalyst consumption.
It is still another object of this invention to provide an improved polymerization process.
It is yet another object of this invention to provide homopolymers of mono-1-olefins and copolymers of at least two different mono-1-olefin(s) that can be processed easily, as indicated by increased branching and a broad molecular weight distribution.
It is still another object of this invention to provide homopolymers of mono-1-olefins and copolymers of at least two different mono-1-olefin(s) that have an increased molecular weight.
In accordance with this invention heterogeneous catalyst systems comprising diimine nickel complexes which further comprise additional ligands selected from the group consisting of xcex1-deprotonated-xcex2-diketones, xcex1-deprotonated-xcex2-ketoesters, halogens and mixtures thereof having a formula selected from the group consisting of Ni(NCRxe2x80x2C6R2H3)2(Y2C3Rxe2x80x32X)2 and Ni(NCRxe2x80x2C6R2H3)2(Y2C3Rxe2x80x32X)Z and methylaluminoxane are provided. Processes to make these catalyst systems also are provided.
In accordance with another embodiment of this invention, slurry polymerization processes comprising contacting ethylene, and optionally one or more higher alpha-olefins, in a reaction zone with heterogeneous catalyst systems comprising diimine nickel complexes which further comprise additional ligands selected from the group consisting of xcex1-deprotonated-xcex2-diketones, xcex1-deprotonated-xcex2-ketoesters, halogens and mixtures thereof in the presence of methylaluminoxane are provided.
In accordance with this invention heterogeneous catalyst systems consisting essentially of diimine nickel complexes which further comprise additional ligands selected from the group consisting of xcex1-deprotonated-xcex2-diketones, xcex1-deprotonated-xcex2-ketoesters, halogens and mixtures thereof and methylaluminoxane are provided. Processes to make these catalyst systems also are provided.
In accordance with another embodiment of this invention, slurry polymerization processes consisting essentially of contacting ethylene, and optionally one or more higher alpha-olefins, in a reaction zone with heterogeneous catalyst systems comprising diimine nickel complexes which further comprise additional ligands selected from the group consisting of xcex1-deprotonated-xcex2-diketones, xcex1-deprotonated-xcex2-ketoesters, halogens and mixtures thereof in the presence of methylaluminoxane are provided.
In accordance with yet another embodiment of this invention, compositions comprising homopolymers of ethylene and copolymers of ethylene and one or more higher alpha-olefins which can be characterized as having high molecular weight, increased branching and a broad molecular weight distribution, are provided.
Catalyst systems of this invention can be characterized as diimine nickel complexes comprising additional ligands selected from the group consisting of xcex2-diketonates, halogens and mixtures thereof having a farmula selected from the group consisting of Ni(NCRxe2x80x2C6R2H3)2(Y2C3Rxe2x80x32X)2 and Ni(NCRxe2x80x2C6R2H3)2(Y2C3Rxe2x80x32X)Z and also represented by general structural formulas as shown below in Compounds I and II, 
wherein R can be the same or different and is selected from the group consisting of branched or linear alkyl or aromatic groups having from about 1 to about 10, preferably from about 1 to about 8, carbon atoms per alkyl group and R can be in any position on the aromatic ring; and
Rxe2x80x2 can be the same or different and is selected from the group consisting of hydrogen and linear, branched, cyclic, bridging, aromatic, and/or aliphatic hydrocarbons, having from about 1 to about 70, preferably from about 1 to about 20, carbon atoms per radical group.
R substituents on the aromatic rings of the diimine nickel complex can be the same or different, and are selected from the group consisting of branched or linear alkyl (aliphatic) or aromatic groups having from about 1 to about 10, preferably from about 1 to about 8, carbon atoms per alkyl group. Although hydrogen can be used, hydrogen can inhibit synthesis of the ligand. R groups having more than about 8 carbon atoms per group can result in a catalyst system with lower activity and/or productivity. While not wishing to be bound by theory, it is believed that larger substituent groups can cause steric hindrance in the catalyst system, thereby which can decrease catalyst system activity and/or productivity and/or ease of synthesis of the catalyst. Exemplary alkyl substituents are selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, benzyl, phenyl groups, and mixtures of two or more thereof. Preferably, the R substituent is an electron-donating species, selected from the group consisting of linear or branched aliphatic groups having from about 1 to about 5 carbon atoms per group. Most preferably, the R groups are both the same and are selected from the group consisting of methyl and isopropyl, due to commercial availability and ease of synthesis of the ligand.
The R group can be in any position, i.e., from 2 to 6, on the aromatic ring. Preferably, the R group, which can be the same or different, is either in the 2 or 6 position, due to ease of synthesis. Most preferably, for best catalytic activity and productivity, both R groups are the same and are in the 2 and 6 positions on the aromatic ring.
Rxe2x80x2 substituents can be the same or different and are selected from the group consisting of hydrogen and branched, linear, cyclic, aromatic or aliphatic radicals having from about 1 to about 70 carbon atoms per radical. Further, the Rxe2x80x2 substituents can be linked, or joined, across the carbon-carbon bridge between the two nitrogen atoms. While not wishing to be bound by theory, it is believed that radicals having more than 70 carbon atoms can add to the steric hindrance of the catalyst systems and hinder catalyst synthesis and/or activity and productivity. Preferably, the Rxe2x80x2 substituent group is selected from the group consisting of hydrogen and branched, linear, cyclic, aromatic or aliphatic radicals having from about 1 to about 20 carbon atoms per radical, due to commercial availability and ease of synthesis of the ligand. Most preferably, the Rxe2x80x2 substituent groups are the same or a link across the carbon-carbon bridge between the nitrogen atoms, and the Rxe2x80x2 substituent is selected from the group consisting of hydrogen and branched, linear, cyclic, aromatic or aliphatic radicals having from about 1 to about 12 carbon atoms per radical, for the reasons given above. Exemplary Rxe2x80x2 substituents include, but are not limited to, hydrogen, methyl, ethyl, propyl, phenyl, taken together acenaphthyl or cyclobutadienyl. Preferably, the Rxe2x80x2 substituents are identical and are selected from the group consisting of hydrogen, methyl and acenaphthyl for best resultant catalyst system activity and productivity.
Rxe2x80x3CYCXCYRxe2x80x3 substituents, or ligands, in which Rxe2x80x3 can be the same or different, on the diimine nickel complex can be the same or different and are selected from the group consisting of xcex1-deprotonated-xcex2-diketones, xcex1-deprotonated-xcex2-ketoesters, halogens and mixtures thereof. The xcex1-deprotonated-xcex2-diketones and xcex1-deprotonated-xcex2-ketoesters can be derived from xcex2-diketone and xcex2-ketoester ligand precursors. Rxe2x80x3 and X can be the same or different and are selected from the group consisting of hydrogen and linear, branched, cyclic bridging, aromatic, aliphatic hydrocarbons, and mixtures thereof having from about 1 to about 70 carbon atoms per radical group, optionally containing atoms other than carbon and hydrogen; and wherein Y and be the same or different and is selected from the group consisting of oxygen, sulfur, or selenium. Further, wherein one Rxe2x80x3 and X are selected from the group consisting of hydrogen and linear, branched, cyclic, bridging, aromatic, aliphatic hydrocarbon radicals, and mixtures thereof having from about 1 to about 70 carbon atoms per radical group, optionally containing atoms other than carbon and hydrogen and wherein the other Rxe2x80x3 is selected from the group consisting of alkoxides of linear, branched, cyclic, bridging, aromatic, and aliphatic hydrocarbon radicals, and mixtures thereof having from about 1 to about 70 carbon atoms per radical group, optionally containing atoms other than carbon and hydrogen. Exemplary ligands precursors include, but are not limited to, compounds selected from the group consisting of 2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, allylacetonacetate, benzoylacetonate, benzoyl-1,1,1-trifluoroacetone, 1,1,1-trifluoro-2,4-pentanedione, 1-chloro-1,1-difluoroacetylacetone methyl-4,4,4-trifluoroacetoacetate, 1,1,1-trifluoro-5,5-dimethyl-2,4-pentanedione, ethyl xcex1-methyl-4,4,4-trifluoroacetoacetate, 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione, and 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione. Preferably, ligand precursors are selected from the group consisting of 2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, 1,1,1-trifluoro-2,4-pentanedione, 1-chloro-1,1-difluoroacetylacetone, methyltrifluoroacetoacetate, 1,1,1-trifluoro-5,5-dimethyl-2,4-pentanedione, and ethyl xcex1-methyl-4,4,4-trifluoroacetoacetate. Most preferably, ligands include, but are not limited to 2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, 1,1,1-trifluoro-2,4-pentanedione, 1-chloro-1,1-difluoroacetylacetone, and 1,1,1-trifluoro-5,5-dimethyl-2,4-pentanedione for best catalysts system activity as well as best polymer product properties.
The group Z, i.e., halogen, of the diimine nickel complex is selected from the group consisting of fluorine, chlorine, bromine and/or iodine. Preferably, the halogen is selected from the group consisting of chlorine and/or bromine for high catalyst activity and productivity. Most preferably, the halogen is chlorine for best catalyst system activity and productivity.
The diimine nickel complex catalyst system disclosed in this application can be prepared by any method known in the art. For example, approximate molar equivalents of a diimine ligand and a nickel compound can be contacted in the presence of any compound that can dissolve both the diimine ligand and nickel compound, either partially or completely. The contacting conditions can be any conditions suitable to effect the formation of a diimine nickel complex. Preferably, for best product results, the diimine ligand/nickel complex mixture is contacted at room temperature under a dry atmosphere for any amount of time sufficient to form the diimine nickel complex. Completion of the formation of the diimine nickel complex can be evidenced by a color change. Generally, contacting times of about 8, and preferably 12 hours are sufficient. Usually, as a result of the preparation procedure, the resultant diimine nickel complex will comprise from about 3 to about 20, preferably from about 5 to about 15, weight percent nickel, based on the total mass of the diimine nickel complex. The presence of oxygen is not thought to be detrimental to this aspect of the preparation procedure.
In general, diimine ligands are contacted with a nickel xcex2-diketonate or nickel xcex2-diketonate halide to form diimine nickel complexes. Typical syntheses of nickel complexes related to those described in this invention can be found in Dieck, H., Svboda, M., and Greiser, T., Z. Naturforsch B: Anorg. Chem. Organ. Chem., Vol. 36b, pp. 823-832 (1981), herein incorporated by reference. Usually, for ease of catalyst system preparation, the diimine ligand is prepared first. The catalyst preparation procedure can vary, depending on the substituents on the diimine ligand. For example, to prepare a specific diimine ligand, wherein Rxe2x80x2 is hydrogen, a three-component mixture is prepared. A two-fold molar excess of aniline, containing the desired R substituents (RnC6H(7-n)N, wherein n=1,2), is contacted with a dialdehyde, such as, for example, glyoxal (CHOCHO), in the presence of a compound capable of being a solvent for both organic and aqueous compounds. Exemplary solvents for both organic and aqueous compounds include, but are not limited to, methanol, ethanol and/or tetrahydrofuran (THF). The mixture can be contacted, preferably refluxed, under any atmosphere to form the desired ligand. Preferably, the mixture is refluxed for at least 10, preferably 20 minutes, cooled and the desired ligand can be recovered. Generally, after refluxing and cooling, the ligand can be recovered in a crystalline form.
To prepare another specific diimine ligand wherein the Rxe2x80x2 group is anything other than hydrogen, a similar procedure can be used. For example, at least a two-fold molar excess of aniline or a substituted aniline can be combined with a compound capable of dissolving both organic and aqueous compounds and a very minor amount of formic acid. Then, about a one molar equivalent of an alpha-diketone (Rxe2x80x2COCORxe2x80x2) can be added to the mixture. The mixture can be stirred, under atmospheric conditions of temperature and pressure until the reaction is complete and the desired ligand is formed. Preferably, water is absent from the reaction mixture. Generally, the reaction will be complete in about 18, preferably 24 hours. A crystalline ligand product can be recovered according to any method known in the art.
The nickel bis(xcex2-diketonate), nickel bis(xcex2-ketoester), nickel xcex2-diketonate halide and nickel xcex2-ketoester halide can be prepared by any method known in the art. Typical syntheses of such nickel complexes can be found in Bullen, G. J., Mason, R., and Pauling, P., Inorganic Chemistry, Vol. 4, pp. 456-462 (1965), herein incorporated by reference. Alternatively, and especially in the case of nickel xcex2-diketonate halides and nickel xcex2-ketoester halides, the salt of the xcex2-diketone or xcex2-ketoester can be prepared then reacted with the correct quantity of nickel halide. A mixture of an appropriate Brxc3x6nsted base, such as but not limited to sodium or potassium hydride or sodium or potassium methoxide, is mixed with a solvent capable of dissolving or becoming miscible with the xcex2-diketone or xcex2-ketoester. Exemplary solvents include toluene, benzene, methanol, or ethanol. One molar equivalent of the xcex2-diketone or xcex2-ketoester is added slowly to this mixture. Reaction is known to occur as evidenced by the evolution of heat and a change in the physical appearance of the mixture. Once all reactants have contacted, reaction times from 4 to 12 hours are sufficient to ensure complete reaction. If the product salt of the xcex2-diketone or xcex2-ketoester is not soluble in the solvent chosen, the solvent is removed by filtration or vacuum and the salt dissolved in a solvent in which it is soluble. Exemplary solvents include methanol and ethanol. This solution is then added to a one half molar equivalent of nickel halide that has been suspended or dissolved in the same solvent or a solvent with which the first solvent is miscible. The preceding reactant ratio results in the formation of the nickel bis(xcex2-diketonate) or nickel bis(xcex2-ketoester). If the nickel xcex2-diketonate halide or nickel xcex2-ketoester halide are desired, the solution is added to one molar equivalent of nickel halide as described. Reaction is known to occur as evidenced by the formation of a soluble green species. Reaction times of 4 to 12 hours are sufficient to ensure complete reaction. The byproduct sodium or potassium halide salt is then removed from the reaction product by filtration and/or centrifugation. The solvent is removed by vacuum to yield the nickel complex used in the nickel diimine complex synthesis.
After formation of a diimine nickel complex, the diimine nickel complex can be recovered by any method known in the art, such as, for example evaporation and/or vacuum filtration of the solvent. Further, if desired, the diimine nickel complex can be further purified by washing. One exemplary wash compound can be heptane. The diimine nickel complex catalyst system can be recovered and used as a solid, heterogeneous catalyst system.
Polymers produced according to the process of this invention can be homopolymers of mono-1-olefins or copolymers of at least two different mono-1-olefins. Exemplary mono-1-olefins useful in the practice of this invention include, but are not limited to mono-1-olefins having from about 2 to about 10 carbon atoms per molecule. Preferred mono-1-olefins include, but are not limited to ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-octene, 1-nonene and 1-decene. If the reaction product is a copolymer, one mono-1-olefin monomer can be polymerized with a mono-1-olefin comonomer which is a different alpha-olefin, usually having from about 3 to about 10, preferably from 3 to 8 carbon atoms per molecule. Exemplary comonomers include, but are not limited to, propylene, 1-butene, butadiene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, and mixtures thereof. Preferably, if the monomer is ethylene, the comonomer is 1-hexene and/or 4-methyl-1-pentene, in order to achieve maximum polymer product toughness. Preferably, if the monomer is propylene, the comonomer is ethylene and/or butadiene in order to achieve maximum polymer product toughness and clarity.
If a comonomer is used, the comonomer can be added to the polymerization reactor, or reaction zone, in an amount within a range of about 1 to about 20 weight percent, preferably within 7 to about 18 weight percent, based on the weight of the ethylene monomer. Most preferably, a comonomer is present in the reaction zone within a range of about 10 to about 16 weight percent, in order to produce a polymer having the most desired physical properties.
Polymerization of the monomer and optional comonomer must be carried out under slurry, also known as loop/slurry or particle form, polymerization conditions wherein the temperature is kept below the temperature at which polymer swells significantly. Slurry polymerization processes are much easier to operate and maintain than other polymerization processes; a polymer product produced by a slurry process can be recovered much more easily. Such polymerization techniques are well-known in the art and are disclosed, for instance, in Norwood, U.S. Pat. No. 3,248,179, the disclosure of which is hereby incorporated by reference.
The slurry process generally is carried out in an inert diluent (medium), such as, for example, a paraffin, cycloparaffin, and/or aromatic hydrocarbon. Preferably, the inert diluent is an alkane having less that about 12 carbon atoms per molecule, for best reactor operation and polymer product. Exemplary diluents include, but are not limited to propane, n-butane, isobutane, n-pentane, 2-methylbutane (isopentane), and mixtures thereof. Isobutane is the most preferred diluent due to low cost and ease of use.
The temperature of the polymerization reactor, or reaction zone, when using isobutane as the reactor diluent, according to this invention, is critical and must be kept within a range of about 5xc2x0 to about 100xc2x0 C. (41xc2x0-212xc2x0 F.) and preferably within a range of about 10xc2x0 to about 70xc2x0 C. (50xc2x0-158xc2x0 F.). Most preferably, the reaction zone temperature is within a range of 20xc2x0 to 60xc2x0 C. (68xc2x0-140xc2x0 F.) for best catalyst activity and productivity. Reaction temperatures below about 10xc2x0 C. can be ineffective for polymerization.
Pressures in the slurry process can vary from about 100 to about 1000 psia (0.76-7.6 MPa), preferably from about 200 to about 700 psia. Most preferably, the reaction zone is maintained at a pressure within a range of 300 to 600 psia for best reactor operating parameters and best resultant polymer product. The catalyst system is kept in suspension and is contacted with the monomer and comonomer(s) at sufficient pressure to maintain the medium and at least a portion of the monomer and comonomer(s) in the liquid phase. The medium and temperature are thus selected such that the polymer or copolymer is produced as solid particles and is recovered in that form. Catalyst system concentrations in the reactor can be such that the catalyst system content ranges from 0.001 to about 1 weight percent based on the weight of the reactor contents.
The catalyst system and methylaluminoxane (MAO) can be added to the reactor in any order to effect polymerization. For example, catalyst system can be added, then some reactor diluent, such as isobutane, followed by MAO, then more diluent and finally, monomer and optional comonomer. However, as stated earlier, this addition order can be varied, depending on equipment availability and/or desired polymer product properties. Preferably, the catalyst system and MAO are not precontacted prior to addition to the polymerization reactor due to a possible decrease in catalyst activity.
The amount of catalyst system and MAO added to the reactor can vary. Generally, a molar excess of MAO is present, relative to the diimine nickel complex. Preferably, the aluminum to nickel (Al:Ni) molar ratio is less than about 1500:1, more preferably within a range of about 50:1 to about 600:1. Most preferably, the molar ratio of aluminum to nickel is within a ratio of 100:1 to 400:1 for best catalyst system activity and productivity.
Two preferred polymerization methods for the slurry process are those employing a loop reactor of the type disclosed in Norwood and those utilizing a plurality of stirred reactors either in series, parallel or combinations thereof wherein the reaction conditions can be the same or different in the different reactors. For instance, in a series of reactors, a chromium catalyst system which has not been subjected to the reduction step can be utilized either before or after the reactor utilizing the catalyst system of this invention.
Polymers produced in accordance with this invention generally have a relatively narrow heterogeneity index (HI), which is a ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) (also expressed as Mn/Mn). Polymers produced in accordance with this invention usually have a HI within a range of about 3 to about 10, preferably within a range of about 3 to about 6, for best indication of processability.
Polymers produced in accordance with this invention are very unique because of a significant amount of short chain branching which can be produced even in the absence of a comonomer added to the reactor. This short chain branching is evidence that some sort of comonomers are produced in-situ in the reactor and are incorporated into the polymer and/or that the catalyst can form short chain branches by rearrangement of the main polymer chain through successive hydride elimination, olefin rotation, and hydride re-addition reactions. This series of steps may not involve discrete intermediates and may rather be a concerted or continuous series of reactions with no distinct intermediates formed. Such rearrangements can be termed xe2x80x9cchain walkingxe2x80x9d. Chain walking can be described by the active metal catalyst, i.e. nickel, xe2x80x9cwalkingxe2x80x9d a distance along the polymer backbone during polymerization and hence, the short chain branch length can be dictated by the rate of ethylene insertion relative to the combined rates of hydride elimination, olefin rotation, and hydride re-addition. Usually polymers produced in accordance with this invention, wherein no comonomer is added to the polymerization reactor comprise up to about 3000, and generally from about 20 to about 3000 short chain branches per 10,000 (or from about 2 to about 300 short chain branches per 1000) backbone carbon atoms of the polymer. Furthermore, the short chain branches produced comprise both odd and even carbon branches, i.e., branches comprising an odd number of carbon atoms per short chain branch, as well as branches comprising an even number of carbon atoms per short chain branch.
If desired, optional addition of one or more comonomers can be added to the polymerization reactor. The affirmatively added comonomers can further increase the amount of short chain branching in the resultant polymer, or copolymer. Polymers produced with the addition of a comonomer can have a greater number of short chain branches in addition to those generated as described above. If a comonomer is affirmatively added to the polymerization reactor, these polymers usually can comprise up to about 3500, and generally from about 20 to about 3500, short chain branches per 10,000 backbone carbon atoms of polymer.
A further understanding of the invention and its advantages is provided by the following examples.